Prior art engines often utilize engine oil for lubricating pistons and cylinders. Engine oil produces pollutants, causing pollution to environment. Prior art engines also comprise numerous moving or wearable parts. Such parts include, but are not limited to, pistons, cylinders, nuts and bolts, pushrods, valves, lifters, cylinder walls, piston pins, rod bearings, rockers, rocker posts, springs, chains, sprockets, sprocket covers, and piston rings. These parts contribute to the issues of increased size and weight, lower reliability and higher costs of manufacturing. Given the aforementioned issues, prior art engines have insufficient environmental safety, reliability and economics in manufacturing.